test(sandbox): add integration tooling

.plans/trap-sandbox/04-integration-tooling.md

@@ -9,13 +9,14 @@ Host tooling (`just`/`npm.just` recipes, `sandbox-serve`, docs) and the cross-si
 **integration** (real craftos ↔ real gateway) plus the **full-boot e2e**.
 
 ## Task checklist
-- [ ] `just/npm.just`: extend `install/build/check/test/test-integration/ci` to cover
+- [x] `just/npm.just`: extend `install/build/check/test/test-integration/ci` to cover
       `tools/trap-sandbox` alongside mcp-bridge; ensure `just install`/`just ci` include it.
-- [ ] `just/opencode.just` (or new recipe): add **`just sandbox-serve`** mirroring `opencode-serve`.
-- [ ] `docs/public-ports.md`: add a `4444` row.
-- [ ] TS integration harness + cases (`tools/trap-sandbox/test-integration/`).
-- [ ] Full-boot e2e.
-- [ ] Gate: `npm run test:integration` green; `just ci` covers both tools.
+      (Symmetric per-tool recipes; `npm-trap-sandbox-ci` removed.)
+- [x] **`just sandbox-serve`** added in new `just/sandbox.just` (warn-only on missing secret).
+- [x] `docs/public-ports.md`: added a `4444` row.
+- [x] TS integration harness + cases (`tools/trap-sandbox/test-integration/`).
+- [x] Full-boot e2e.
+- [x] Gate: `npm run test:integration` green; `just ci` covers both tools.
 
 ## Tooling
 - `just/npm.just`: extend recipes (install/build/check/test/test-integration/ci) to cover
@@ -44,6 +45,7 @@ contains `sandboxOk: true`. Bounded by generous timeouts.
 ## Verification gate (also the project-level acceptance)
 - `npm test`, `npm run test:integration`, `npm run lint`/`check` clean in `tools/trap-sandbox`.
 - `just _craftos-test` runs `tests/sandbox.lua`; `just ci` covers both tools.
-- Manual: `just sandbox-serve`; in-game `set sandbox.url ws://<host>:4444/gateway` (+
+- Manual: `just sandbox-serve`; in-game `set sandbox.url ws://<host>:4444` (origin only —
+  libsandbox appends `/gateway`) (+
   `set sandbox.password <secret>` if `SANDBOX_PASSWORD` set), reboot, `sandbox health` →
   `sandboxOk: true` / `opencodeOk: …`.

.plans/trap-sandbox/trap-sandbox-gateway-spec.md

@@ -38,7 +38,7 @@ verification gate is green.
   in place, Lua unit tests green via `just _craftos-test`. *Implements the Protocol contract.*
 - [x] **M3 — Packages** ([03-packages](./03-packages.md)): legacy renamed, new `trapos-sandbox`
   package + meta bump wired; `packages/index.json` consistent.
-- [ ] **M4 — Integration & tooling** ([04-integration-tooling](./04-integration-tooling.md)):
+- [x] **M4 — Integration & tooling** ([04-integration-tooling](./04-integration-tooling.md)):
   `just` recipes, `docs/public-ports.md`, TS integration harness + full-boot e2e green.
   *Requires both sides — build last.*
 

Justfile

@@ -6,6 +6,7 @@ import 'just/install.just'
 import 'just/npm.just'
 import 'just/craftos.just'
 import 'just/opencode.just'
+import 'just/sandbox.just'
 import 'just/test.just'
 import 'just/check.just'
 

docs/public-ports.md

@@ -7,6 +7,7 @@ TrapOS public production services use the `4242-4244` TCP range. Keep local deve
 | `4242` | opencode server HTTP API | Production/public port for `opencode serve`. Local/dev examples may still use opencode's default `4096`. |
 | `4243` | ComputerCraft bridge WebSocket | Production/public equivalent of the local bridge link default `3001`. Use `CC_LINK_PORT=4243` for production bridge deployments. |
 | `4244` | Reserved | Free public production port reserved for a future service. Do not assign it casually in local tooling. |
+| `4444` | trap-sandbox gateway | Fastify service (`tools/trap-sandbox`) exposing the `trapos-cloud-gateway` WebSocket at `/gateway`. Sits **outside** the `4242-4244` range on purpose (4244 stays reserved). Default `SANDBOX_PORT`; serve with `just sandbox-serve`. |
 
 ## Local Vs Production
 

just/npm.just

@@ -10,28 +10,40 @@ npm-install-trap-sandbox:
     npm install --prefix tools/trap-sandbox/
 
 # Build Node-based repository tools.
-npm-build:
+npm-build: npm-build-mcp-bridge npm-build-trap-sandbox
+
+npm-build-mcp-bridge:
     npm run build --prefix tools/mcp-bridge
 
+npm-build-trap-sandbox:
+    npm run build --prefix tools/trap-sandbox/
+
 # Check Node-based repository tools.
-npm-check:
+npm-check: npm-check-mcp-bridge npm-check-trap-sandbox
+
+npm-check-mcp-bridge:
     npm run check --prefix tools/mcp-bridge
 
+npm-check-trap-sandbox:
+    npm run check --prefix tools/trap-sandbox/
+
 # Run Node-based tool tests.
-npm-test:
+npm-test: npm-test-mcp-bridge npm-test-trap-sandbox
+
+npm-test-mcp-bridge:
     npm test --prefix tools/mcp-bridge
 
+npm-test-trap-sandbox:
+    npm test --prefix tools/trap-sandbox/
+
 # Run Node-based tool integration tests.
-npm-test-integration:
+npm-test-integration: npm-test-integration-mcp-bridge npm-test-integration-trap-sandbox
+
+npm-test-integration-mcp-bridge:
     npm run test:integration --prefix tools/mcp-bridge
 
-# Run Node-based tool CI.
-npm-ci:
-    npm run test:ci --prefix tools/mcp-bridge
-
-# Run trap-sandbox CI.
-npm-trap-sandbox-ci:
-    npm --prefix tools/trap-sandbox/ run test:ci
+npm-test-integration-trap-sandbox:
+    npm run test:integration --prefix tools/trap-sandbox/
 
 # Build generated artifacts.
 build: npm-build

just/sandbox.just

@@ -0,0 +1,18 @@
+# Serve the trap-sandbox gateway (port 4444) for remote/in-game attachment using
+# repo-local .env secrets. Mirrors `opencode-serve`, but auth is optional: an unset
+# SANDBOX_PASSWORD means the gateway runs with auth disabled (warn, do not fail).
+[positional-arguments]
+sandbox-serve *args:
+    #!/usr/bin/env bash
+    set -euo pipefail
+    repo='{{justfile_directory()}}'
+    if [ -f "$repo/.env" ]; then set -a; . "$repo/.env"; set +a; fi
+    if [ -z "${SANDBOX_PASSWORD:-}" ]; then
+        printf '%s\n' 'sandbox-serve: SANDBOX_PASSWORD unset in .env — gateway auth disabled' >&2
+    fi
+    export SANDBOX_PASSWORD="${SANDBOX_PASSWORD:-}"
+    export OPENCODE_SERVER_PASSWORD="${OPENCODE_SERVER_PASSWORD:-}"
+    export OPENCODE_URL="${OPENCODE_URL:-http://127.0.0.1:4242}"
+    export SANDBOX_HOST="${SANDBOX_HOST:-0.0.0.0}"
+    export SANDBOX_PORT="${SANDBOX_PORT:-4444}"
+    exec npm run dev --prefix tools/trap-sandbox -- "$@"

just/test.just

@@ -1,5 +1,5 @@
 # Local CI entry point used by Git hooks. Pass args through to CraftOS tests.
-ci *args: check-craftos check check-packages npm-build npm-test npm-trap-sandbox-ci
+ci *args: check-craftos check check-packages npm-build npm-test
     @just _craftos-test {{args}}
     @just test-integration
 

tools/trap-sandbox/test-integration/auth.test.ts

@@ -0,0 +1,47 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+import { formatFailure, startCraftos, startSandbox } from "./harness.js";
+
+const SECRET = "s3cr3t-canary";
+
+test("hello with the wrong secret is rejected in-band (unauthorized)", async () => {
+  const sandbox = await startSandbox({ sandboxPassword: SECRET });
+  const craftos = startCraftos("gateway-client.lua", {
+    computerId: 7,
+    computerLabel: "auth-bad",
+    shellArgs: [sandbox.baseUrl, "wrong-secret", "auth"],
+  });
+  try {
+    const result = await craftos.done;
+    assert.match(
+      result.output,
+      /__SANDBOX_HELLO__ ok=false code=unauthorized/,
+      formatFailure("expected hello ok=false code=unauthorized", result.output),
+    );
+  } finally {
+    craftos.abort();
+    await craftos.done.catch(() => undefined);
+    await sandbox.close();
+  }
+});
+
+test("hello with the correct secret succeeds", async () => {
+  const sandbox = await startSandbox({ sandboxPassword: SECRET });
+  const craftos = startCraftos("gateway-client.lua", {
+    computerId: 7,
+    computerLabel: "auth-ok",
+    shellArgs: [sandbox.baseUrl, SECRET, "auth"],
+  });
+  try {
+    const result = await craftos.done;
+    assert.match(
+      result.output,
+      /__SANDBOX_HELLO__ ok=true/,
+      formatFailure("expected hello ok=true", result.output),
+    );
+  } finally {
+    craftos.abort();
+    await craftos.done.catch(() => undefined);
+    await sandbox.close();
+  }
+});

tools/trap-sandbox/test-integration/duplicate.test.ts

@@ -0,0 +1,52 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+import { formatFailure, startCraftos, startSandbox, waitFor } from "./harness.js";
+
+// Two real computers with the same traposId (id:label): newest-wins. After both
+// complete hello, exactly one registration exists; aborting the newest clears it
+// (the displaced first computer is in its 5s reconnect backoff), proving the newest
+// connection is the one that's registered.
+test("duplicate traposId is resolved newest-wins", async () => {
+  const sandbox = await startSandbox();
+  const TRAPOS_ID = "9:dup";
+
+  const first = startCraftos("gateway-client.lua", {
+    computerId: 9,
+    computerLabel: "dup",
+    shellArgs: [sandbox.baseUrl, "-", "idle"],
+  });
+  const second = startCraftos("gateway-client.lua", {
+    computerId: 9,
+    computerLabel: "dup",
+    shellArgs: [sandbox.baseUrl, "-", "idle"],
+  });
+
+  try {
+    await waitFor(() => first.snapshot().includes("__SANDBOX_READY__"), 12_000, "first connected");
+    assert.ok(sandbox.registry.has("local", TRAPOS_ID), "first should be registered");
+
+    await waitFor(() => second.snapshot().includes("__SANDBOX_READY__"), 12_000, "second connected");
+    // Newest-wins: still exactly one registration for the shared id.
+    assert.equal(sandbox.registry.count(), 1, "exactly one registration after the duplicate");
+    assert.ok(sandbox.registry.has("local", TRAPOS_ID));
+
+    // Aborting the newest clears the entry; the displaced first is in reconnect
+    // backoff (~5s) and has not re-registered yet.
+    second.abort();
+    await second.done.catch(() => undefined);
+    await waitFor(() => sandbox.registry.count() === 0, 3_000, "newest was the live registration");
+  } catch (error) {
+    throw new Error(
+      formatFailure(
+        error instanceof Error ? error.message : String(error),
+        `first:\n${first.snapshot()}\nsecond:\n${second.snapshot()}`,
+      ),
+      { cause: error },
+    );
+  } finally {
+    first.abort();
+    second.abort();
+    await Promise.all([first.done.catch(() => undefined), second.done.catch(() => undefined)]);
+    await sandbox.close();
+  }
+});

tools/trap-sandbox/test-integration/full-boot.test.ts

@@ -0,0 +1,27 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+import { formatFailure, startCraftos, startFakeOpencode, startSandbox } from "./harness.js";
+
+// Full-boot e2e: a real CraftOS computer runs the real servers/sandbox.lua daemon
+// (driven by sandbox.* settings) and the real `sandbox health` program against the
+// real gateway, with a healthy fake-opencode behind it.
+test("full boot: settings -> daemon -> sandbox health prints sandboxOk/opencodeOk true", async () => {
+  const opencode = await startFakeOpencode({ status: 200 });
+  const sandbox = await startSandbox({ sandboxPassword: "boot-secret", opencodeUrl: opencode.url });
+  const craftos = startCraftos("full-boot.lua", {
+    computerId: 11,
+    computerLabel: "boot",
+    shellArgs: [sandbox.baseUrl, "boot-secret"],
+    timeoutMs: 20_000,
+  });
+  try {
+    const result = await craftos.done;
+    assert.match(result.output, /sandboxOk:\s*true/, formatFailure("expected sandboxOk: true", result.output));
+    assert.match(result.output, /opencodeOk:\s*true/, formatFailure("expected opencodeOk: true", result.output));
+  } finally {
+    craftos.abort();
+    await craftos.done.catch(() => undefined);
+    await sandbox.close();
+    await opencode.close();
+  }
+});

tools/trap-sandbox/test-integration/harness.ts

@@ -0,0 +1,172 @@
+import { spawn } from "node:child_process";
+import { createServer } from "node:http";
+import { mkdtemp, rm } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { dirname, join } from "node:path";
+import { fileURLToPath } from "node:url";
+import type { AddressInfo } from "node:net";
+import { createApp, type Config } from "../src/app.js";
+import type { GatewayRegistry } from "../src/modules/trapos-cloud-gateway/registry.js";
+
+const HERE = dirname(fileURLToPath(import.meta.url));
+const LUA_DIR = join(HERE, "lua");
+const REPO_ROOT = join(HERE, "../../..");
+
+export type Sandbox = {
+  registry: GatewayRegistry;
+  // Gateway origin (no path). This is what `sandbox.url` expects: libsandbox appends
+  // `/gateway` itself. Pass this to the Lua scripts.
+  baseUrl: string;
+  // Full WS endpoint (origin + `/gateway`), for direct ws clients.
+  socketUrl: string;
+  close: () => Promise<void>;
+};
+
+export type SandboxOptions = {
+  sandboxPassword?: string;
+  opencodeUrl?: string;
+  requestTimeoutMs?: number;
+};
+
+// Real Fastify gateway on an ephemeral port. Mirrors index.ts's wiring but with a
+// silent logger and test-supplied config (never reads process.env).
+export async function startSandbox(opts: SandboxOptions = {}): Promise<Sandbox> {
+  const config: Config = {
+    host: "127.0.0.1",
+    port: 0,
+    sandboxPassword: opts.sandboxPassword,
+    requestTimeoutMs: opts.requestTimeoutMs ?? 5_000,
+    opencodeUrl: opts.opencodeUrl,
+    opencodeUsername: "opencode",
+    opencodeServerPassword: undefined,
+    logger: { level: "silent" },
+  };
+
+  const { app, registry } = await createApp(config);
+  await app.listen({ host: config.host, port: config.port });
+  const { port } = app.server.address() as AddressInfo;
+
+  const baseUrl = `ws://127.0.0.1:${port}`;
+  return {
+    registry,
+    baseUrl,
+    socketUrl: `${baseUrl}/gateway`,
+    close: () => app.close(),
+  };
+}
+
+export type FakeOpencode = {
+  url: string;
+  close: () => Promise<void>;
+};
+
+// Tiny stand-in for the opencode server. The probe issues `GET /config`; we reply
+// with `status` (default 200) on every path so opencodeOk can be steered per test.
+export async function startFakeOpencode(opts: { status?: number } = {}): Promise<FakeOpencode> {
+  const status = opts.status ?? 200;
+  const server = createServer((_req, res) => {
+    res.writeHead(status, { "content-type": "application/json" });
+    res.end("{}");
+  });
+  await new Promise<void>((resolve) => server.listen(0, "127.0.0.1", resolve));
+  const { port } = server.address() as AddressInfo;
+  return {
+    url: `http://127.0.0.1:${port}`,
+    close: () => new Promise<void>((resolve) => server.close(() => resolve())),
+  };
+}
+
+export async function waitFor(predicate: () => boolean, timeoutMs: number, label: string): Promise<void> {
+  const deadline = Date.now() + timeoutMs;
+  while (Date.now() < deadline) {
+    if (predicate()) {
+      return;
+    }
+    await sleep(50);
+  }
+  throw new Error(`waitFor timed out: ${label}`);
+}
+
+export type CraftosResult = {
+  status: number | null;
+  signal: NodeJS.Signals | null;
+  output: string;
+};
+
+export type CraftosHandle = {
+  done: Promise<CraftosResult>;
+  abort: () => void;
+  // Stdout/stderr accumulated so far; lets a test await a marker line while the
+  // process is still running (e.g. wait for "__SANDBOX_READY__" before acting).
+  snapshot: () => string;
+};
+
+// Spawn headless CraftOS-PC running a Lua script from test-integration/lua, with the
+// repo mounted read-only (/apis, /servers, /programs, /trapos) so the scripts can
+// require the real libsandbox / servers / programs.
+export function startCraftos(
+  luaName: string,
+  opts: { computerId?: number; computerLabel?: string; shellArgs?: string[]; timeoutMs?: number } = {},
+): CraftosHandle {
+  const timeoutMs = opts.timeoutMs ?? 15_000;
+  const controller = new AbortController();
+  const chunks: Buffer[] = [];
+
+  const done = (async (): Promise<CraftosResult> => {
+    const dataDir = await mkdtemp(join(tmpdir(), "trap-sandbox-it-"));
+    const watchdog = setTimeout(() => controller.abort(), timeoutMs);
+    try {
+      const args: string[] = [
+        "--directory", dataDir,
+        "--headless",
+        "--mount-ro", `/staging=${LUA_DIR}`,
+        "--mount-ro", `/trapos=${REPO_ROOT}`,
+        "--mount-ro", `/apis=${join(REPO_ROOT, "apis")}`,
+        "--mount-ro", `/servers=${join(REPO_ROOT, "servers")}`,
+        "--mount-ro", `/programs=${join(REPO_ROOT, "programs")}`,
+      ];
+      if (opts.computerId !== undefined) {
+        args.push("--id", String(opts.computerId));
+      }
+      if (process.platform === "darwin") {
+        args.push("--rom", "/Applications/CraftOS-PC.app/Contents/Resources");
+      }
+      args.push("--exec", buildExecCode(luaName, opts.shellArgs ?? [], opts.computerLabel));
+
+      const child = spawn("craftos", args, { signal: controller.signal });
+      child.stdout.on("data", (d: Buffer) => chunks.push(d));
+      child.stderr.on("data", (d: Buffer) => chunks.push(d));
+
+      const result = await new Promise<{ status: number | null; signal: NodeJS.Signals | null }>((resolve) => {
+        child.once("close", (code, signal) => resolve({ status: code, signal }));
+        child.once("error", () => resolve({ status: null, signal: null }));
+      });
+
+      return { status: result.status, signal: result.signal, output: Buffer.concat(chunks).toString("utf8") };
+    } finally {
+      clearTimeout(watchdog);
+      await rm(dataDir, { recursive: true, force: true });
+    }
+  })();
+
+  return { done, abort: () => controller.abort(), snapshot: () => Buffer.concat(chunks).toString("utf8") };
+}
+
+export function formatFailure(message: string, craftosOutput: string): string {
+  return ["\x1b[31mFAIL\x1b[0m " + message, "--- craftos output ---", craftosOutput.trimEnd(), "----------------------"].join("\n");
+}
+
+function buildExecCode(luaName: string, shellArgs: string[], computerLabel?: string): string {
+  const programPath = luaName.startsWith("/") ? luaName : `/staging/${luaName}`;
+  const parts = [luaQuote(programPath), ...shellArgs.map(luaQuote)];
+  const setup = computerLabel === undefined ? "" : `os.setComputerLabel(${luaQuote(computerLabel)}); `;
+  return `${setup}shell.run(${parts.join(", ")})`;
+}
+
+function luaQuote(value: string): string {
+  return `'${value.replaceAll("\\", "\\\\").replaceAll("'", "\\'")}'`;
+}
+
+function sleep(ms: number): Promise<void> {
+  return new Promise((resolve) => setTimeout(resolve, ms));
+}

tools/trap-sandbox/test-integration/health.test.ts

@@ -0,0 +1,49 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+import { formatFailure, startCraftos, startFakeOpencode, startSandbox } from "./harness.js";
+
+test("probe_gateway reports opencodeOk=true when opencode is healthy", async () => {
+  const opencode = await startFakeOpencode({ status: 200 });
+  const sandbox = await startSandbox({ opencodeUrl: opencode.url });
+  const craftos = startCraftos("gateway-client.lua", {
+    computerId: 7,
+    computerLabel: "health-ok",
+    shellArgs: [sandbox.baseUrl, "-", "health"],
+  });
+  try {
+    const result = await craftos.done;
+    assert.match(
+      result.output,
+      /__SANDBOX_HEALTH__ sandboxOk=true opencodeOk=true/,
+      formatFailure("expected sandboxOk=true opencodeOk=true", result.output),
+    );
+  } finally {
+    craftos.abort();
+    await craftos.done.catch(() => undefined);
+    await sandbox.close();
+    await opencode.close();
+  }
+});
+
+test("probe_gateway reports opencodeOk=false when opencode is unhealthy", async () => {
+  const opencode = await startFakeOpencode({ status: 500 });
+  const sandbox = await startSandbox({ opencodeUrl: opencode.url });
+  const craftos = startCraftos("gateway-client.lua", {
+    computerId: 7,
+    computerLabel: "health-bad",
+    shellArgs: [sandbox.baseUrl, "-", "health"],
+  });
+  try {
+    const result = await craftos.done;
+    assert.match(
+      result.output,
+      /__SANDBOX_HEALTH__ sandboxOk=true opencodeOk=false/,
+      formatFailure("expected sandboxOk=true opencodeOk=false", result.output),
+    );
+  } finally {
+    craftos.abort();
+    await craftos.done.catch(() => undefined);
+    await sandbox.close();
+    await opencode.close();
+  }
+});

tools/trap-sandbox/test-integration/lua/full-boot.lua

@@ -0,0 +1,30 @@
+-- Full-boot e2e: replicate the real boot path (startup/servers.lua) closely enough
+-- to prove the whole stack works end to end. Sets the sandbox.* settings, creates
+-- the global event loop, runs the REAL servers/sandbox.lua daemon, then under
+-- parallel waits for the connection and runs the REAL `sandbox health` program.
+--
+-- Args (via shell.run): url, secret ('' => none).
+-- NOTE: shell.run drops empty-string args; the harness passes '-' for "no secret".
+local args = { ... };
+local url = args[1];
+local secret = args[2];
+
+settings.set('sandbox.url', url);
+if secret and secret ~= '' and secret ~= '-' then
+  settings.set('sandbox.password', secret);
+end
+
+_G.bootEventLoop = require('/apis/eventloop')();
+
+-- Start the real daemon (reads sandbox.url/sandbox.password, opens the WS).
+shell.run('/servers/sandbox.lua');
+
+parallel.waitForAny(
+  function() _G.bootEventLoop.runLoop(true); end,
+  function()
+    os.pullEvent('trapos_sandbox_connected');
+    shell.run('/programs/sandbox.lua', 'health');
+  end
+);
+
+os.shutdown();

tools/trap-sandbox/test-integration/lua/gateway-client.lua

@@ -0,0 +1,77 @@
+-- Integration-test driver: exercises the REAL trapos-sandbox client (libsandbox)
+-- against a real gateway. Reuses startSession/request/onMessage so the test covers
+-- production client code + CraftOS JSON serialization quirks.
+--
+-- Args (via shell.run): url, secret, scenario.
+--   url      gateway origin, e.g. ws://127.0.0.1:PORT (daemon appends /gateway)
+--   secret   shared secret ('' => none)
+--   scenario health | auth | idle  (default: health)
+--
+-- Each scenario prints a single sentinel line the TS test asserts on.
+-- NOTE: shell.run re-tokenizes its arguments, so empty-string args are dropped and
+-- positions shift. The harness passes '-' as the "no secret" sentinel instead of ''.
+local args = { ... };
+local url = args[1];
+local secret = args[2];
+if secret == '' or secret == '-' then secret = nil; end
+local scenario = args[3] or 'health';
+
+local createSandbox = require('/apis/libsandbox');
+local createEventLoop = require('/apis/eventloop');
+
+_G.bootEventLoop = createEventLoop();
+local sandbox = createSandbox();
+local session = sandbox.startSession({
+  eventloop = _G.bootEventLoop,
+  url = url,
+  secret = secret,
+  os = os,
+});
+
+-- Connect, probe the gateway, report opencodeOk.
+local function runHealth()
+  os.pullEvent('trapos_sandbox_connected');
+  local ok, payload = sandbox.request('probe_gateway');
+  if ok then
+    print('__SANDBOX_HEALTH__ sandboxOk=' .. tostring(payload.sandboxOk)
+      .. ' opencodeOk=' .. tostring(payload.opencodeOk));
+  else
+    print('__SANDBOX_HEALTH__ error=' .. tostring(type(payload) == 'table' and payload.code));
+  end
+end
+
+-- Poll the hello outcome: ready => ok:true, terminal lastError => ok:false code.
+local function runAuth()
+  local deadline = os.epoch('utc') + 8000;
+  while os.epoch('utc') < deadline do
+    if session.isReady() then
+      print('__SANDBOX_HELLO__ ok=true');
+      return;
+    end
+    local err = session.lastError();
+    if err then
+      print('__SANDBOX_HELLO__ ok=false code=' .. tostring(err));
+      return;
+    end
+    os.sleep(0.1);
+  end
+  print('__SANDBOX_HELLO__ ok=false code=timeout');
+end
+
+-- Connect and stay registered so the TS side can drive the gateway->computer
+-- direction (reverse ping) or assert registry state (duplicate newest-wins).
+local function runIdle()
+  os.pullEvent('trapos_sandbox_connected');
+  print('__SANDBOX_READY__ ' .. sandbox.traposId(os));
+  os.sleep(10);
+end
+
+local scenarios = { health = runHealth, auth = runAuth, idle = runIdle };
+local run = scenarios[scenario] or runHealth;
+
+parallel.waitForAny(
+  function() _G.bootEventLoop.runLoop(true); end,
+  run
+);
+
+os.shutdown();

tools/trap-sandbox/test-integration/reverse-ping.test.ts

@@ -0,0 +1,28 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+import { formatFailure, startCraftos, startSandbox, waitFor } from "./harness.js";
+
+// Exercises the gateway -> computer direction: the gateway sends a `ping`
+// gateway_request and the real libsandbox client answers with a computer_response.
+test("gateway->computer reverse ping is answered by the client", async () => {
+  const sandbox = await startSandbox();
+  const craftos = startCraftos("gateway-client.lua", {
+    computerId: 7,
+    computerLabel: "ping",
+    shellArgs: [sandbox.baseUrl, "-", "idle"],
+  });
+  try {
+    await waitFor(() => sandbox.registry.has("local", "7:ping"), 12_000, "computer registered");
+    const payload = await sandbox.registry.request("local", "7:ping", "ping");
+    assert.deepEqual(payload, { traposId: "7:ping" });
+  } catch (error) {
+    throw new Error(
+      formatFailure(error instanceof Error ? error.message : String(error), craftos.snapshot()),
+      { cause: error },
+    );
+  } finally {
+    craftos.abort();
+    await craftos.done.catch(() => undefined);
+    await sandbox.close();
+  }
+});